1. Field of the Invention
The present invention is directed to a fixing device for fixing toner images onto a receiving material, and to a method of removing debris from the surface of an endless fixing member of such a fixing device.
2. Description of the Related Art
In an electronic printer, where toner particles are deposited on a surface in image form and are subsequently transferred to a receiving material, such as paper, the toner particles must be fixed onto the receiving material in order to render the images permanent. This fixing process is often achieved by a combination of heat and pressure applied in a fixing nip. For example, the receiving material, onto which unfixed toner particles have already been deposited, is passed through the fixing nip where an increased temperature and pressure serve to fix the image permanently to the receiving material. Alternatively, a transfer surface carrying the unfixed toner particles is fed through the fixing nip together with the receiving material, whereby the increased temperature and pressure cause the transfer of the toner particles from the transfer surface to the receiving material and the simultaneous fixing of the toner image thereon.
Particularly when the recording medium is paper or a fibrous material, debris in the form of dust and/or fibers, or other impurities can be transferred back from the recording medium to the transfer surface. Together with possible residual toner particles, these debris and other impurities are referred to herein as contaminants. The contaminants negatively affect the transfer properties and the overall lifetime of the transfer surface and can result in a severe image quality degradation. Furthermore, in constructions in which the transfer surface is in contact with the photoreceptor of an image forming station directly or by way of one or more further transfer members, the situation might even get worse as these contaminants might transfer back to the photoreceptor. Consequently to assure high quality printing, the cleaning of the transfer surface is important.
A fixing device is known, for example from European patent specification EP 149860 (Ocxc3xa9-Nederland BV) for fixing toner images onto a receiving material. The device comprises a fixing roller urged into contact with a pressure roller to form a fixing nip there-between through, which a copy sheet passes. A perforated cleaning roller is in contact with the surface of the fixing roller to remove debris therefrom. Toner particles are applied to the cleaning member to render the surface tacky. A disadvantage of this arrangement is that due to the interrupted surface of the cleaning roller, caused by the perforations, several revolutions are required to ensure that each part of the fixing roller is contacted by the tacky surface.
In a fixing device described in U.S. Pat. No. 4,018,555 (Thettu/Xereox Corpotation), a fuser roller is urged into contact with a backup roller to form a fixing nip there between through which copy paper or substrate material passes. An internally heated cleaning roller having a tacky surface is positioned in contact with the surface of the fixing roller remove debris therefrom. The cleaning roller can be rejuvenated by the application thereto of a tacky polymeric adhesive.
U.S. Pat. No. 4,705,388 (Huntjens et al./Ocxc3xa9-Nederland BV) describes a method and apparatus for determining when a layer of tacky material present on a cleaning roller needs to be rejuvenated. The period rejuvenation of the tacky layer described in this patent is found to lead to inconsistent cleaning characteristics and/or a build up of excess tacky material on the cleaning roller.
U.S. Pat. No. 4,013,400 (Thettu et al./Xerox Corporation) describes a cleaning apparatus for a heat and pressure fuser. A cleaning roller having a tacky surface contacts the fuser roller to remove contaminants therefrom. Polymer material is applied to the cleaning roller from a moving web.
We have found that the above mentioned fixing devices are not as successful at removing debris from the fixing nip as may be desired for high quality work. In particular, these prior proposals do not provide for the effective removal of contaminants form the cleaning roller, thereby limiting the lifetime of the cleaning roller.
Thus it is an object of the present invention to provide a device and method in wich an improved removal of debris is possible. In particular, it is an object of the present invention to improve the overall transfer efficiency and image quality by removing impurities, which are transferred back from the recording medium. It is a further object of the present invention to increase the uptime of the print engine or copier by in-situ and continuously rejuvenating the tacky surface of the cleaning roller by providing refreshment material and simultaneously removing excess and/or contaminated tacky surface material therefrom.
In one embodiment of the invention, the fixing device for fixing toner images onto a recording medium comprises an endless fixing member urged into contact with an endless counter member to form a fixing nip there between through which a recording medium path extends, a cleaning roller having a surface in contact with the surface of the fixing member downstream of the fixing nip, the surface carrying a layer of tacky cleaning material, a controllable applicator unit for continuously providing fresh cleaning material to the cleaning roller, and a spindle contacting the cleaning roller surface for transporting the fresh cleaning material from the applicator unit across the roller and for transporting the contaminated tacky cleaning material towards an edge of the cleaning roller.
In another embodiment, the invention comprises a method of removing contaminants from the surface of an endless fixing member of a fixing device in which the fixing member is urged into contact with a counter member to form a fixing nip there between through which the recording medium passes comprising contacting the fixing member surface at a cleaning nip with a cleaning roller having a tacky surface layer of cleaning material, thereby to transfer contaminants from the fixing member to the tacky surface, continuously applying fresh cleaning material to the cleaning roller to rejuvenate the tacky surface, and contacting the cleaning roller surface with a revolving spindle to distribute the fresh cleaning material across the cleaning roller and to transport the contaminated cleaning material to an edge of the cleaning roller.